This disclosure relates generally to the oilfield industry and to downhole tools used in wellbores for anchoring tool strings to these wellbores. This disclosure relates more particularly to slip assemblies of such downhole tools, for example slip assemblies of frac plugs, bridge plugs or packers.
Fracing is a process that continues to grow in popularity, as it is known to enhance hydrocarbon production of tight reservoirs. Typically, the fracing process involves the use of frac plugs for isolating a section of the wellbore below or beyond a target zone in order to treat that zone. After setting of the frac plug, fracing fluid is pumped or injected into the target zone at high pressure, resulting in fractures or “cracks” propagating in the formation, and ultimately in valuable hydrocarbons being more easily and abundantly produced through the formation fractures. Once the target zone is treated, the frac plug may be unset, or may be destructed with a drill bit.
Setting frac plugs involves anchoring the frag plugs in the wellbore, typically against an inner wall of a tubular. To anchor a frac plug, a slip assembly including a cone and a slip ring is typically used. The cone may include external fins that are integral to and run axially along the cone. The slip ring may include at least one axial slot, which facilitates subsequent breaking up of the slip ring into individual slip segments. Each slip segment may include a channel that is adapted to mate with an external fin of the cone. As the slip ring traverses the cone, the channels of the slip segments ride on the fins encouraging the slip ring to break apart along the slots into the slip segments. While presenting advantages, these fins often cause additional complications. It is not unusual to see these fins destroyed by the movement of the slips, to have the slip jump over a fin after the first slot breaks, or to have the slots in certain regions remain intact. Also, proper setting of the frac plug relies on the fracturing of numerous weak points and on the movement of the slip segments in unison to achieve a homogeneous contact pressure between the tubular, the fractured ring segments, and the cone. Thus, proper setting is often conditioned by a repeatable break-up of the slip ring.
Thus, there is a continuing need in the art for methods and apparatus for reliably anchoring downhole tools. The features utilized to guide the slip segments are preferably robust. The break-up of the slip ring into ring segments is preferably achieved consistently.